Method of continuous casting



P 1967 K. G. SPEITH ETAL 3,

METHOD OF CONTINUOUS CASTING Filed Oct. 2, 1963 Ad -vex United StatesPatent 3,315,323 METHOD OF CONTINUOUS CASTING Karl Georg Speith andAdolf Bungeroth, Duisburg, and

Klaus Frenken, Essen-Verden, Germany, assignors to MannesmannAktiengesellschaft, Dusseldorf, Germany, a corporation of Germany FiledOct. 2, 1963, Ser. No. 313,249 Claims priority, application Germany,Oct. 4, 1962,

M 54,396; June 18, 1963, M 57,209

1 Claim. (Cl. 22-200.1)

The invention relates to a method for continuous casting.

The manufacture of continuous billets from metals with high-meltingpoints by continuous casting plants giving satisfactory surfaces stillinvolves many difliculties. The causes of the surface defects are themarginal crusts and oxidation films which arise at the edge of the bathsurface and are drawn along by the billet, forming scabs or scarfs.

In this specification metals with high melting points are understood tobe steel, iron and so-called base nonferrous metals and their alloys.

The object of the invention is toobtain satisfactory billets, withperfect surfaces in particular, when casting any grade of metal bycontinuous casting, the amount of slag on the bath surface being assmall as possible.

According to the invention it is proposed that after pouring on, as soonas the fluid metal, such as steel, in r the mould has reached a certainpredetermined level required for casting, a powdery covering material isapplied to the bath surface in an amount sufficient to cover thissurface completely, and that at least part of this material shouldremain powdery while the rest may melt so that after a few minutes ofthe temperatures prevailing in the top of the billet a fluid slag layeris formed whose surface tension is such that the mould wall is notwetted.

The quantity of covering powder may be such that only part of it meltswhile the rest stays on top of it in a solid, powdery state, reducingthe heat radiation of the slag and preventing the slag from forming acoating. The quantity applied may then be 3 to 10 grams per :squarecentimeter of the billet surface area, and preferably 3 to 6 grams persquare centimeter, the larger quan- I tities being associated with thelonger casting times. Results so far obtained indicate that in steelcasting a maximum of .7 kg. and an average of .4 to .6 kg. of coveringpowder is needed per tonne of steel. If because of a very unstablepouring jet the slag surface is covered with steel spatters or ifbecause of unexpectedly long casting times the covering material meltsthe slag may be skimmed off and the covering material applied again.

The casting surface in continuous casting moulds can be covered withloosely poured, that is, drippable, powdery materials which, partlymelting and forming slag, make a slag layer which is thin compared withthe powdery layer above it and is tough enough not to touch the mouldwall. These covering powders for use in extrusion have a relatively highmelting point, preferably above 1400 C., in case of partial melting ahigh viscosity, preferably above 100 poises, and a relatively highsurface tension. They are used in layers of moderate thickness, with themould lubrication turned ofl, up to about 50 mm. on the casting surfacein a moved sliding mould. If the covering powder melts where it touchesthe casting surface, it is essential that the tough slag layer inpermanent contact with the powder above and gradually forming from thisshould be only moderately thick (up to about 25 mm.).

total Good results were obtained with covering materials of thefollowing composition:

Percent Si0 35-50 A1 0 20-40 CaO 2-10 MgO 0-5 Na O+K O 3-12 Fe-l-Mn(total content of the oxides) 5-15 C (total content) 3-13 P, S .5

A change in composition within the limits given if possible if, forexample, when greatly varying grades are being cast, the castingtemperature fluctuates over a wide range. Other compositions of thecovering material are possible if they only form a suitable viscous slagat the casting temperatures concerned, part of the quantity appliedremaining in a powdery state.

Another covering powder has the following composition:

Percent SiO 41.0 Al O +TiO 23.5 CaO 3.0 MgO 2.0 Na O+K O 3.7 Fe-i-Mlltdtl3 P,S .3 Heat loss 7 It is possible to use fine-ground powder ofsubstances which do not melt at steel casting temperatures. Thesesubstances may for examples consist of CaO or A1 0 or other high-meltingoxides of the alkaline-earth metals or of the group of rare earths,alone or in a mixture, preferably with an admixture of up to 30% ofpulverized graphite, coal or coke.

The use of such covering powders has the result that the heat lossesfrom the casting surface and with them the risk of cold run formationare greatly reduced, and that oxidation of the casting surface isprevented and that the slag skimmings usually appearing on the castingsurfaces are taken up by the covering and prevented from passingradially over the casting surface edge and prevented from. forminginclusions on or in the surface and method of using them described canthe invention be satisfactorily used. Because the thickness of the toughslag layer arising in the case of partial melting of the covering powderis kept down as stated earlier, and because of its relatively largesurface tension, the mould wall, which is favorably cold and dry, is nottouched by the tough slag. To make sure that when tough slag is formedthere is, even over long periods, no wetting of the mould wall whichmight greatly endanger the casting process, it is essential that themould movement continually bring traces of the easily flowing, not lumpycovering powder into the space between the mould'wall and the edge ofthe tough slag. The liberation, resulting from heating, of repellentgases which, as is well known, adhere to the large surfaces of finepowders in considerable amounts also helps to prevent the tough slagfrom approaching and sticking to the mould wall and to cause then,friction-reducing layers of gas to form between the billet skin and themould wall.

The method according to the invention is particularly suitable forcasting steels containing aluminum. Contrary to all expectations, it wasfound that these steels, despite the high A1 content of the slag, had amuch lower content of aluunina inclusions than steels cast in the usualway. The surface of the billet, moreover, was always in very goodcondition, although steels containing aluminum are notorious forinvolving special casting problems as regards the surface condition.

It was also found that in spite of the high carbon content of thecovering coating there is no carbonization of the steel. Moreover,surprisingly, the good results obtained are not adversely affected bythe omission of the mould lubrication otherwise needed, regardless ofthe grade of steel.

The powdery covering material is preferably fed to the bath surface bymeans of a neutral gas through a ring conduit with nozzles on the upperedge of the mould. The number of nozzles depends on the size of thebillet. Other known mechanical feeding means may, of course, be usedinstead.

To prevent the slag from being washed into the billet by the pouring jetand the slag from being enriched with granulated material, a ceramicpipe, for example of zircon silicate, with a suitable diameter may befixed to the mould or the feed pipe for the covering powder so as toproject into the top of the billet.

The invention will now be described, by way of example only, withreference to the accompanying drawings. In these:

FIG. 1 shows a continuous casting mould; and

FIG. 2 shows another embodiment of a continuous casting mould, with thefeed device for the covering material omitted.

A continuous casting mould 1 (FIG. 1) contains a continuous billet 2which has solidified at the edges. Above this there is a conventionaldistributing vessel 3, from which the fluid steel drops in a free fallto the bath surface through a spout 4. Above the mould 1 there is a ringconduit 6 with nozzles 5 through which the covering mixture which is tobe applied to the bath surface is sent by means of a neutral gas. Thecrosssection of the ring conduit 6 and the number of nozzles 5 depend onthe quantity to be supplied and the crosssection of the billet. Part ofthe powdery covering material applied to the bath surfare there forms atough slag 7, while the rest stays above this in a powdery state 8.

The embodiment shown in 'FIG. 2 also has the fluid part 7 and powderypart 8 of the covering material on the bath surface. To prevent thecovering material from being carried away by the pouring jet, a ceramicpipe 9 is suspended in the mould 1. The lower end of this reaches intothe top of the billet, and its diameter is such that it does notinterfere with the free fall of the pouring jet.

The method as a whole has a number of quite considerable advantages overthe state of the art. By adding the slag mixture in a solid state nospecial melting devices are needed for the slag. Feeding is completelysafe and much easier to carry out. The smallness of the amount that hasto be added is a considerable saving. As the method can be used withoutany mould lubrication there are advantages over conventional lubricationon the grounds of this saving alone, and with slag lubrication the costof subsequent removal of the slag layer from the casting surface issaved. Above all, however, there is the certainty of good surfaces atall times, for no change in the consistency of the slag is caused bynon-metallic inclusions coming up out of the steel.

We wish it to be understood that we do not desire.

to be limited to the exact details of construction shown and described,for obvious modifications will occur to a person skilled in the art.

Having thus described the invention, what we claim as new and desire tobe secured by Letters Patent is as follows.

We claim:

In a method of continuously casting, in an open ended casting mould,metals of high-melting points and their alloys, respectively, the stepscomprising applying a powdery covering material to the upper metal bathsurface after the upper metal bath surface has reached a substantiallypredetermined height in the casting mould, at least some of saidmaterial being operative to melt, thereby forming a covering slag on aportion of said surface, where the covering slag layer is not more than25 mm. thick and has a viscosity of over 100 poises, so that thecovering slag layer does .not touch the mould wall, the gap between thecovering slag layer and the mould wall is being filled with the powderymaterial, and the powdery layer remaining on top of the covering slaglayer is at least as thick as the covering slag layer.

References Cited by the Examiner UNITED STATES PATENTS 2,304,258 12/1942Junghans 22.2-00.1 2,568,525 9/1951 Waddington et al. 22-57.2 X2,737,696 3/ 1956 Shields 22-215 2,760,859 8/1956 Graf 94 2,797,9907/1957 Froats 75-94 2,825,947 3/1958 Goss 22-200 1 3,034,186 5 1962Holhouser 22-200.l 3,089,209 5/1963 Phillips et a1. 22-2001 3,153,82010/1964 Criner 22-57.2 3,167,829 2/1965 Hess et al 22-.57.2

FOREIGN PATENTS 835,084 5/1960 Great Britain.

J. SP-ENCCER OVERHOLSER, Primary Examiner. R. S. ANNEAR, AssistantExaminer.

